Haifei Deng

Large magnetoresistance in (In, Zn)As/InAs p-n junction

We study the magnetotransport property of a (In, Zn)As/InAs p-n junction and observe a breakdown behavior in the reverse bias region. This breakdown behavior can be attributed to two different electronic processes: the trap-assisted tunneling at moderate reverse voltage and the impact ionization at high reverse voltage. The former gives rise to a positive magnetoresistance, and a maximum of 226% is obtained at room temperature. The latter induces a very large positive magnetoresistance and its maximum of 428% is observed at a reverse voltage of 1.32 V.

A succinct method to generate multi-type HCV beams with a spatial spiral varying retardation-plate

A simple novel and practical scheme is presented to generate high-power cylindrical vector (HCV) beams with a 36-segment spiral varying retardation-plate sandwiched between two quarter-wave plates (QWPs). Four kinds of HCV beams, such as radially polarized beam and azimuthally polarized beam, are formed by simply rotating two QWPs. A segmented spiral varying phase-plate with isotropy is used to modulate spatial phase distribution to generate in-phase HCV beams. The intensity distributions and polarizing properties of HCV beams are investigated and analyzed in detail. It is demonstrated experimentally that the system can effectively generate multi-type HCV beams with high purity up to 99%, and it can be manufactured as cylindrical vector beam converter commercially.

Multiple-slit diffraction of high-polarization-order cylindrical vector beams

Multiple-slit diffraction properties of high-polarization-order cylindrical vector (HCV) beams were studied in detail. Flowerlike intensity distributions are obtained after HCV beams passing through a linear polarizer. The intensity distributions of single-slit, double-slit, triple-slit and four-slit diffraction of high-order radially polarized (HRP) beams and high-order azimuthally polarized (HAP) beams are obtained, and analyzed with different slit spacings. It was indicated that diffraction fringes of HCV beams were not continuous. Faultage appeared, and the faultage number was 2P+1, which was only related to the polarization order number P, but independent of slit number N. It was found that the obvious and clear diffraction phenomenon would be obtained in the conditions 2ω≈ (N+1)D, N≥2 in which ω 0 is the beam waist radius and D is the slit spacing. This study can be used to detect and analyze higher-order vector beams. Besides, it helps to design special diffractive optical elements.

The Cooling Performance Improvement of First Wall Using He/CO2 Binary Mixtures Gas for CN HCCB TBM

Abstract The Helium (He) gas Cooled Ceramic Breeder (HCCB) test blanket module (TBM) is the primary option of the Chinese TBM program. In order to enhance the cooling ability of the first wall (FW) of the HCCB TBM and reduce the circulation power, a binary mixtures gas of He gas and additive CO2 deserves to be another option for the coolant of the blanket, based on high temperature gas-cooled reactors which are a generation-IV fission reactor concept, when it is reported that forced convective heat transfer can be enhanced by means of binary mixing with unreactive gas (e.g., CO2, molecular weight 44). This technique can significantly enhance the plant’s overall efficiency and reduce the cost of electricity. In order to evaluate the cooling performance of the He/CO2 binary mixtures gas and its circulation power in the FW of the HCCB TBM, a three-dimensional computational fluid dynamics (CFD) numerical simulation, combined experimental research method is applied. The results reveal that under the condition of the cooling requirements of the FW (e. g., maximum temperature, radial temperature gradient) similar to the pure He gas, the flow velocity and circulation power of the He/CO2 binary mixtures gas (mole fraction 0.4) are reduced by 70% and 87%, respectively. It implies that the thermal efficiency of a He-cooled blanket system can be fairly enhanced by means of this technique. In the near future experiment plan, it should be tested to validate the correlative cooling scheme of the HCCB TBM, in which the pure He gas and He/CO2 binary mixtures gas are used as coolant, respectively, at our High-Pressure Helium-Cooled Loop facility. The CFD numerical results will be selected as the reference for the experiments. A new approach may be provided for cooling the high heat flux components of a fusion reactor.

Arbitrary polarized beams generated and detected by one phase-only LC-SLM

Arbitrary polarized beams, including homogeneously polarized beams and cylindrical vector beams, have been generated by an experimental setup with one phase-only liquid crystal spatial light modulator, and a four-path method was demonstrated to measure the polarization degree of detected beams. Besides, another method was proposed to measure the polarization directions of cylindrical vector beams. The polarized states can be calculated by controlling the spatial light modulator and optical intensity obtained from a CCD. The generation setup and detection methods have simple structure and low cost, and they are available for multi wavelength input beams, and the detection methods can realize real-time and on-line measurement.

Optical vortex beams generated by a phase-only LC-SLM and double-slit interference analysis

Vortex beams with integral and fractional topological charges are generated by an experimental setup with one phase-only liquid crystal spatial light modulator which efficiently modulates the phase retardation distributions of input beam. The intensity distributions and double-slit interference of vortex beams with integral and fractional topological charges are investigated in detail. Tilt appears in double-slit interference fringes of vortex beams. The fringe tilt amounts in the intermediate region are proportional to the topological charge l of vortex beams. The double-slit interference method can be utilized to determine the topological charge of vortex beams.